I'm running SyncBackSE V8.5.97.0 and have encountered this problem. In my case, restarting the computer failed to fix it, (i.e the up-down arrows are still greyed out) so I'm currently unable to change the order of profiles.

Problem solved. The group was set to run profiles in parallel, hence the option to arrange their order was automatically disabled.
The check-box for 'Run profiles in parallel' was also greyed out, so under 'Click For Options' I selected 'Load defaults'. This cleared all my selected profiles, but I was then able to re-select them and use the up-down arrows to arrange the order.

Not sure if this is a feature or a bug, but it would be nice if the order of profiles in a group could be rearranged also when they are set to run in parallel. Obviously the order doesn't matter in that case, but you may still want to display them in a certain order that's not necessarily alphabetic.